The present embodiments relate generally to calorimeters that may be used to characterize materials such as pharmaceuticals, biologicals, proteins, cellular organisms, food products, industrial chemicals and other materials.
Calorimeters are instruments that may be used to measure changes in the energy of a sample of a material by measuring the heat flow between the sample and its surroundings. Examples of calorimeters include differential scanning calorimeters (DSCs) that may be used to measure heat flows associated with heating or cooling a material, or with thermal transitions in materials, and isothermal titration calorimeters (ITCs) that may be used to measure heat as it is absorbed or released during a reaction between two chemicals. DSCs generally have at least one sample cell and at least one reference cell. In a typical DSC measurement, the temperature of the sample cell and of the reference cell is increased or decreased in a controlled manner, although some experiments or measurements may be done at a single temperature. In temperature ranges in which the sample does not undergo a transition, the heat capacity of the sample may be measured by measuring the differential heat flow needed to heat (or cool) the sample compared to the reference. Also, when the sample is heated or cooled through an exothermic or endothermic phase transition, for example, the differential heat flow to or from the sample compared to the heat flow to or from the reference may be used to calculate the enthalpy of the transition.
ITCs generally have a sample cell and a reference cell. ITCs may operate on the power compensation principle, in which the difference in the amount of power required to keep the sample cell and the reference cell at the same temperature is measured. This difference in power is a measure of the heat absorbed or released during a measurement. In a typical ITC measurement, the sample cell contains a first material. Small quantities of a second material are injected gradually and sequentially into the sample cell using, for example, a syringe. When the molecules of the second material react with or bind with the molecules of the first material, heat is either absorbed or released. The ITC's sensors detect the temperature difference between the sample cell and a reference cell due to the binding reaction, and provide feedback to the heaters for the sample and for the reference. The heaters then compensate for the difference between the sample cell and the reference cell, bringing the temperature of the sample cell equal to the temperature of the reference cell. The difference in the power applied to the sample compared to the power applied to the reference needed to achieve this compensation may be used as a measure of the heat absorbed or released during the measurement.